Epigenetic asymmetry of imprinted genes in plant gametes

Plant imprinted genes show parent-of-origin expression in seed endosperm, but little is known about the nature of parental imprints in gametes before fertilization. We show here that single differentially methylated regions (DMRs) correlate with allele-specific expression of two maternally expressed genes in the seed and that one DMR is differentially methylated between gametes. Thus, plants seem to have developed similar strategies as mammals to epigenetically mark imprinted genes.     

Clonogenic growth of acute non-lymphocytic leukemia cells in serum-free medium

We devised a serum-free medium for growth of leukemic colony-forming units (CFU-L), enriched with albumin, transferrin, lipids, insulin, hydrocortisone and oligoelements. Blast cells from 15 patients affected by acute non-lymphocytic leukemia were grown in this medium in the presence of human placental conditioned medium obtained under serum-free conditions (sfHPCM). Their clonogenic growth was comparable with that obtained in a serum-containing system. Furthermore, when serum-free cultures were carried out in absence of sfHPCM, either CFU-L growth was prevented or, if clones were obtained, the cultures showed a marked decrease in clonogenicity, indicating their strict dependence on growth factors.     

Miniature eye movements enhance fine spatial detail

Our eyes are constantly in motion. Even during visual fixation, small eye movements continually jitter the location of gaze. It is known that visual percepts tend to fade when retinal image motion is eliminated in the laboratory. However, it has long been debated whether, during natural viewing, fixational eye movements have functions in addition to preventing the visual scene from fading. In this study, we analysed the influence in humans of fixational eye movements on the discrimination of gratings masked by noise that has a power spectrum similar to that of natural images. Using a new method of retinal image stabilization, we selectively eliminated the motion of the retinal image that normally occurs during the intersaccadic intervals of visual fixation. Here we show that fixational eye movements improve discrimination of high spatial frequency stimuli, but not of low spatial frequency stimuli. This improvement originates from the temporal modulations introduced by fixational eye movements in the visual input to the retina, which emphasize the high spatial frequency harmonics of the stimulus. In a natural visual world dominated by low spatial frequencies, fixational eye movements appear to constitute an effective sampling strategy by which the visual system enhances the processing of spatial detail.     

A new nurse frog from Southwestern Amazonian highlands,with notes on the phylogenetic affinities of Allobates alessandroi (Aromobatidae)

ABSTRACT

Few studies have focused on the diverse fauna of southwestern Brazilian Amazonia. This region, spared from large-scale human occupation until the second half of the twentieth century, has been threatened by expanding agriculture, logging, and mining. Here, we describe a new nurse frog (Allobates, Aromobatidae) from the open highland habitats of Serra dos Pacaás Novos, one of the few large remnants of relatively intact native vegetation in the Brazilian state of Rondônia. The new species is diagnosed by its metallic orange dorsal colouration, weakly expanded discs on hands, and presence of two subarticular tubercles on Finger IV. A phylogenetic analysis based on DNA sequence data recovered the new species as more closely related to nurse frogs from the Madeira and Tapajós River basins; this pattern may reflect a history of dispersal uphill from a lowland ancestor. Our results also indicate that the generic assignment of Allobates alessandroi (Grant and Rodriguez, 2001), a high-elevation species from the Andes of Peru, needs to be reassessed; we discuss the phylogenetic affinities of this species based on morphological attributes.

http://www.zoobank.org/urn:lsid:zoobank.org:act:79131D82-B1B6-455D-AD9A-676D7E0783BC     

The organs of prey capture and digestion in the miniature predatory bivalve Spheniopsis brasiliensis (Anomalodesmata: Cuspidarioidea: Spheniopsidae) expose a novel life-history trait

Spheniopsis brasiliensis, from depths of 17–148 m off the southern Atlantic coast of Brazil, is a predator of epipsammic micro-crustaceans which it sucks into the infra-septal chamber using a raptorial inhalant siphon and internally generated hydrostatic suction forces. Prey items, which include ostracods, are thought to be pushed into the funnel-shaped mouth using the foot. The stomach is capacious with a short style sac conjoined briefly with the mid gut and possessing a stubby crystalline style. Internal stomach architecture is simplified, with no identifiable sorting areas (unlike other cuspidarioids) and lined virtually completely by a gastric shield. The exoskeletal remains of digested prey are held in the posterior end of the stomach and not in a specialised waste storage pouch as in the con-familial Grippina coronata. The mid gut, hind gut and rectum are all extremely narrow and, thus, only the smallest of faeces can be accommodated and transmitted for anal discharge. Spheniopsis brasiliensis, like G. coronata is a self-fertilising simultaneous hermaphrodite with encapsulated lecithotrophic eggs brooded internally. Both taxa are thus ovovivaporous. It is also believed that both taxa are univoltine so that larvae and the exoskeletal prey remains are all released post mortem. Cuspidariids are generally regarded as dioecious but, recently, Cardiomya costellata has been shown to be a non-brooding simultaneous hermaphrodite. The distinguishing characters between cuspidariids and spheniopsids thus appear to be their differing reproductive strategies and life history traits.     

The mass of the missing baryons in the X-ray forest of the warm-hot intergalactic medium

Recent cosmological measurements indicate that baryons comprise about four per cent of the total mass-energy density of the Universe, which is in accord with the predictions arising from studies of the production of the lightest elements. It is also in agreement with the actual number of baryons detected at early times (redshifts z > 2). Close to our own epoch (z < 2), however, the number of baryons detected add up to just over half (approximately 55 per cent) of the number seen at z > 2 (refs 6-11), meaning that about approximately 45 per cent are 'missing'. Here we report a determination of the mass-density of a previously undetected population of baryons, in the warm-hot phase of the intergalactic medium. We show that this mass density is consistent, within the uncertainties, with the mass density of the missing baryons.